Advocates say studies have not identified why some years see more deaths than others.

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So far in 2014, 15 children have died from heat stroke because they were left in hot cars, according to KidsAndCars, a national nonprofit that works to prevent harm to children in and around vehicles.

When police in Connecticut announced this week that a child had died alone inside a hot car, it was the latest in a string of such deaths across the nation over the past month.

Six children died in June under similar circumstances in the U.S. The case receiving the most national attention is unfolding in suburban Atlanta, where a father is charged with murder for intentionally leaving his 22-month-old son alone in the back of the family SUV. The father, Justin Ross Harris, wanted a "child-free life," according to authorities. Harris claims he was unaware his son was in the back seat when he drove to work.

The six reported deaths last month are down from nine deaths that occurred last June. Still, advocates say the rate remains troubling and more should be done to educate parents and protect kids.

So far in 2014, 15 children have died from heat stroke because they were left in hot cars, according to KidsAndCars.org, a national nonprofit that works to prevent harm to children in and around vehicles. By their count, 44 children died of vehicular heat stroke last year, up from 33 in 2012.

"We wanted to ensure that people understood the dangers involved in not only leaving a child unattended in a car, but even in leaving a car unlocked," Lt Paul Vance of Connecticut Police's department of emergency services and public protection said. He added that kids in the summer play outdoors more often, where they have increased access to cars.

There have been six reported incidents of children being locked hot cars in Connecticut in the last two weeks, the one in Ridgefield on Monday resulting in death. Up until last month, Connecticut had a record of only four reported hot car child deaths since data began being collected in 1990, according to KidsAndCars' data.

"This is a parent's worst nightmare," said Amy Jones, a 32-year-old Connecticut mother and middle school teacher. Her child turned 2 in May.

"It's sad no matter what their age, but especially when you hear about a child of similar age to your own," Jones said.

Twenty states have unattended child in vehicle laws on the books, according to Golden Gate Weather Services. Connecticut's law charges guardians who endanger their children in hot cars with a felony depending on the circumstances. Tennessee, which already had a law in place, added a good Samaritan bill in June that allows a stranger to break into a car if they see an unattended child in danger.

"What we are truly asking is for the public to be our eyes and ears," Vance said. "When you pull into the supermarket and see a child locked in a car, contact law enforcement. We can determine if it's a true emergency, especially in these days of hot, humid, horrific weather."

But even in milder temperatures children are still at risk. The National Highway Traffic Safety Administration warns that even on days with temperatures in the 60s, a car's internal temperature can rise above 110 degrees, and children's bodies warm faster than adults.

"Studies on thermal injury to children show that 'dry heat' temperatures, within a closed vehicle, can become dangerous to small children and infants in only minutes,” Connecticut State Police said in Tuesday's statement. "A high level of humidity can reduce that time by one half."

Could Technology Fix the Problem?

Fennell wants to see more proactive approaches to the issue.

“The child should never be left there in the first place. You’re waiting and hoping for a perfect stranger to help your child,” she said. “It is going to take technology to change this.”

Cars alert drivers and passengers when their seatbelt is unbuckled, when their door isn’t fully closed, or when the gas is running low, Fennell said. But they don’t alert you when you leave a child in the car.

“If you back away and look at it, it’s more important to save a dead car battery than a dead baby,” Fennell said.

The National Highway Traffic and Safety Administration has found that current warning systems to detect children left in cars are unreliable, according to research from July 2012.

"I don't know if there's technology that will ever exist," Jones said. She suggests parents should get into the habit of leaving things that are important to them, such as a phone or wallet, in the backseat of the car so the driver won't leave the car without looking in the back.

"Leave something that belongs to you, not something for your child. You can just as easily forget your diaper bag," Jones said.

That's the message that KidsAndCars.org and similar organizations, including SafeCar.gov, are spreading through the awareness campaign Look Before You Lock. They are encouraging drivers with children in the car to adopt simple routines, such as leaving an object in the back seat that the driver will reach for before leaving the car.

"There have been 15 deaths this year. We don't want to contribute to that," Vance said. "We want people to understand that defenseless children need to be taken care of, they need to be remembered, they can’t be forgotten. Certainly that keeps them out of harm's way."